*{
  margin: 0;
  padding: 0;
}
.y1{height:400px;
  width:1200px;
  background-color:red;
  margin: 50px auto;
  position: relative;
}
.images{
  width: 100%;
  height: 100%;
  background-color: red;
  list-style: none;
  position:relative;
}
.images>li{
  width: 100%;
  height: 100%;
  background-color: cadetblue;
  position: absolute;
  left: 0;
  top: 0;
  display: none;
}
.images>li.t1{
  display: block;
}
.left,
.right{
  width: 50px;
  height: 50px;
  background-color: rgba(0,0,0,0.5);
  color: #fff;
  text-align: center;
  line-height:40px;
  position: absolute;
}
.left{
  border-radius:0 20px 20px 0;
  left: 0;
  top: 50%;
  transform: translateY(-50%);
  }
.right {
  border-radius: 20px 0 0 20px;
  right: 0;
  top: 50%;
  transform: translateY(-50%);
}
.pointer{
  width: fit-content;
  height: 12px;
  //background-color: green;
  position: absolute;
  bottom: 15px;
  left: 50%;
  transform: translateX(-50%);
}
.pointer>.s1{
  width: 12px;
  height: 12px;
  margin-right: 4px;
  border: 1px solid rgba(0,0,0,.05);
  background:rgba(255,255,255,.4);
  display: inline-block;
  border-radius: 50%;
}
.pointer>.s1.s2{
  background-color:#ffffff;
  width: 9px;
  height: 9px;
  position: relative;
  top: 2px;
  left: 0px;
  border: 3px solid rgba(0,0,0,.1);
}
.pointer>.s1.s3{
  background-color:#ffffff;
  width: 9px;
  height: 9px;
  position: relative;
  top: 2px;
  left: 0px;
  border: 3px solid rgba(0,0,0,.1);
}